My research associates, postdoctoral fellow, graduate students, and I conduct research along two principal lines: 1) photoreceptors and 2) cytodifferentiation. Under the former we continue to sample photoreceptors in animal phyla not yet well explored, further our efforts to determine the effects of light and darkness upon the ultrastructure of light-sensitive cells, continue our investigation of the function of unique 800 A vesicles in the photoreceptoral cells of molluscan eyes, study regeneration of ocelli in seastars, analyze the sensitivity of different strata in the retina of a jumping spider to different wavelengths of light, study the effects of vitamin A deficiency on receptoral cells in the eyes of a snail (Helix aspersa); determine the ultrastructural effects of severing the optic nerve in Helix; examine the ultrastructure of pineal transplants in the anterior chamber of the eye of a house sparrow. The studies in embryology, principally by my graduate students, will be in the area of early ultrastructural differentiation in amphibian and chick embryos. BIBLIOGRAPHIC REFERENCES: Brandenburger, J.L., R.M. Eakin, and C.T. Reed. Effects of light- and dark-adaptation on the photic microvilli and photic vesicles of the pulmonate snail Helix aspersa. Vision Res., 20 MS pages, 10 figs, 1976. Ermak, T., and R.M. Eakin. Fine structure of the cerebral and pygidial ocelli in Chone ecaudata (Polychaeta: Sabellidae). Jour. Ultrastruct. Res., 54: 243-260, 22 figs, 1976.